Cardinality

In mathematics, the cardinality of a set is a measure of the "number of elements of the set".

For example, the set A = {2, 4, 6} contains 3 elements, and therefore A has a cardinality of 3.

Description

There are two approaches to cardinality: one which compares sets directly using bijections and injections, and another which uses cardinal numbers.

The cardinality of a set is also called its size, when no confusion with other notions of size is possible.

The cardinality of a set A is usually denoted | A |, with a vertical bar on each side; this is the same notation as absolute value and the meaning depends on context. Alternatively, the cardinality of a set A may be denoted by n(A), A, card(A), or # A.

See also

• Aleph number
• Beth number
• Bijection
• Cardinal number
• Cardinality of the continuum
• Countable set
• Injective function
• Ordinality
• Set (mathematics)

External links

• Cardinality @ Wikipedia